The proposed research will test the hypothesis that following its incorporation into the egg, enlargement of the sperm nucleus is coordinated with the activity of the maternal chromatin, i.e., changes in nucleoplasmic interactions affecting the status/function of the maternal chromatin also influence the pattern of sperm nuclear enlargement at fertilization. Formulation of such a hypothesis is based on recent observations demonstrating that sperm nuclear enlargement does not proceed at a uniform rate in eggs inseminated at an arrested stage of meiosis but consists of phases, temporally correlated with major changes in the activity of the maternal chromatin. The presence of distinct phases in the rate of sperm nuclear enlargement suggests that different regulatory processes occur in a specific sequence and are responsible for transforming the sperm nucleus into a pronucleus. The possible mechanisms which comprise each of these phases, how they are regulated and related to one another and conditions modulating activity of the maternal chromatin are aspects to be explored. Investigations will be conducted to determine the kinetics of sperm nuclear enlargement in eggs that can be inseminated at different periods of meiotic maturation. Meiotic maturation of the maternal chromatin will be perturbed by agents having known mechanisms of action, e.g., metabolic and protein synthesis inhibitors, and the rates of sperm nuclear enlargement will be analyzed. In conjunction with these investigations studies will be carried out to examine the possible relation of specific proteins, newly synthesized during fertilization, to processes of meiotic maturation and sperm nuclear transformations. These studies will provide further evidence that specific periods of sperm nuclear enlargement are coupled with the status (condensed/dispersed) of the maternal chromatin. Possible mechanisms regulating sperm nuclear transformations, meiotic maturation, and how the male- and female- derived chromatin become synchronized with respect to events involving first mitosis and the initiation of cell cycle events characteristic of cleaving embryos will be elucidated.